Note: Page contains spoilers for the whole novel.
Zhao Yunlan is the Chief of the SIU in Dragon City and the Guardian.
He is a powerful magic user. He has had the ability to see ghosts since he was born, and at times in the past hasn't always been able to distinguish between ghosts and living people, and therefore treats ghosts and living people equally.
People are routinely surprised by his cleverness and hardworking mentality, because he presents an easygoing and undisciplined front. E.g. in chapter 40. Wang Zheng thinks to herself: 'she always thought that [...] he is probably not the hardworking type. But in only a few days, he already knows the Hanga tribe so well.'
This becomes even more notable later in the novel. Shen Wei notes that if Zhao Yunlan knows a little, he will find out the whole thing. The Hell judge is scared of how much Zhao Yunlan has figured out. Zhao Yunlan 'has the thickest skin possible, and is as sly as a fox. He has three godly skills: being shameless, stalling, and avoiding the topic... even one of those can quickly drive a man to drink. In short, he’s the stuff of the judge's nightmares.' chapter 70. Zhao Yunlan is very good at extrapolating when he has not figured out much yet and then making it seem like he knows a lot more than he does to milk people for information.
Zhao Yunlan is described in chapter 1 as young, handsome, slender and tall, with upright shoulders, thick eyebrows, deep eye sockets, and a high nose. He looks serious and in authority, but he can switch to a very friendly demeanor in an instant.
In chapter 2, he is described from the point of view of a police officer: tall, slender and handsome, 'like a model from a fashion advertisement'. His outfit is derided as not very pleasing: 'a scruffy shirt, only half-buttoned, half of it tucked in and the other half not'. His hairstyle is compared to a bird’s nest.
But nobody can criticize him because he is the Chief. ('Chief Zhao is the Chief after all, no matter how messy he looks. Even if he ran naked on the street, lower tiered officers would probably have to praise him for trendsetting.' chapter 2)
Zhao Yunlan is not good at remembering to eat or get new things. As he cannot cook anything other than boiling water for tea and ramen, he tends to eat take-out.
Iron Goddess tea is one of the types of tea he has at his house.
He also drinks a lot of alcohol, both socially and when he has taken in a lot of new information.
He also smokes cigarettes. When things get stressful, he smokes an entire pack in one go.
He also isn't good at folding up his clothes.
He is friendly with people and ghosts when he wants something from them. He will burn joss money (Hell money) for ghosts and Diyu people when he wants something. He burns it for the Hell judge when he meets with him and for a bookseller ghost when he is going to ask information from her. He will call people brother and then get drunk with them.